scholarly journals Nature of Dust Grains in the Atmosphere of Comet Ashbrook

1980 ◽  
Vol 90 ◽  
pp. 259-262 ◽  
Author(s):  
O. V. Dobrovolsky ◽  
N. N. Kiselev ◽  
G. P. Chernova ◽  
F. A. Tupieva ◽  
N. V. Narizhnaja
Keyword(s):  
Dust Grains ◽  
Opposition Effect ◽  
Small Phase ◽  
Phase Angles ◽  
Anomalous Polarization

Anomalous polarization at small phase angles is confirmed as a common feature of dusty cometary atmospheres. The opposition effect is detected and interpreted as evidence of similarity between grains covering interplanetary, cometary and asteroidal surfaces. The prevailing radii of dust grains in the comet's atmosphere are estimated to be 0.15-0.19 μm.

Saturn rings: divisions, gaps and ringlets from ground-based telescopes

1984 ◽  
Vol 75 ◽  
pp. 147-154 ◽  
Author(s):  
Audouin Dollfus
Keyword(s):  
Phase Angle ◽  
Volume Density ◽  
Light Curves ◽  
High Magnification ◽  
Density Dependent ◽  
Opposition Effect ◽  
Small Phase ◽  
Saturn's Rings ◽  
Phase Angles ◽  
Zero Phase

ABSTRACTThe high magnification visual telescopic observation of Saturn’s rings exhibits divisions, gaps and bright sub-rings. B. Lyot gave a first description of these features. Later, with still more resolving telescopes, we improved the analysis of the ring features. Some gaps and concentric bright or dark sub-rings are phase angle dependent; the steep luminance peaks of their light curves around zero phase angle are volume-density dependent (opposition effect); the overall result produces changes in the shapes and intensities of these features at small phase angles, which are analysed.

scholarly journals The contribution of atmospheric aerosols to the Martian opposition effect

1971 ◽  
Vol 40 ◽  
pp. 166-169
Author(s):  
Jaylee M. Mead
Keyword(s):  
Atmospheric Aerosols ◽  
Mie Scattering ◽  
The Other ◽  
Spherical Particles ◽  
Refractive Indices ◽  
Opposition Effect ◽  
Absorbing Materials ◽  
Small Phase ◽  
Ice Water ◽  
Phase Angles

Mie scattering calculations have been made for atmospheric aerosols having various indices of refraction to determine their possible contribution to a Martian opposition effect, such as that reported by O'Leary in 1967. Neither substances with a real index between 1.20 and 1.50, such as ice, water, or solid CO2, nor highly absorbing materials, such as limonite, can produce the observed effect. Submicron-sized spherical particles with refractive indices of 1.55 to 2.00 do, on the other hand, exhibit a marked increase in reflectivity at small phase angles and might be responsible for the enhanced brightness at the shorter wavelengths.

scholarly journals Longitudinal variations, the opposition effect and monochromatic albedos for Mars

1971 ◽  
Vol 40 ◽  
pp. 141-155
Author(s):  
William M. Irvine ◽  
James C. Higdon ◽  
Susan J. Ehrlich
Keyword(s):  
Phase Curve ◽  
Central Meridian ◽  
Opposition Effect ◽  
Small Phase ◽  
Longitudinal Variations ◽  
The Mean ◽  
Phase Angles ◽  
Narrow Bands ◽  
Zero Phase ◽  
Phase Phase

Observations of Mars previously reported in 10 narrow bands between 3150 Å and 1.06 μ and in UBV are analyzed for brightness variations which correlate with longitude of the central meridian. Such an effect is found for λ ≥ 5000 Å, with some evidence for such a correlation at λ = 4570 Å. The data are then corrected to the mean (over longitude) brightness and a linear phase curve fitted to those observations with phase angle i ≥ 15°. An opposition effect (anomalous brightening at small phase angles) is found for wavelengths λ ≤ 5500 Å, in contrast to a result previously reported. The magnitude at zero phase, phase coefficient, and monochromatic albedo are computed for Mars as a function of wavelength.

scholarly journals Opposition effect on S-type asteroid (25143) Itokawa

2018 ◽  
Vol 616 ◽  
pp. A178 ◽  
Author(s):  
Mingyeong Lee ◽  
Masateru Ishiguro
Keyword(s):  
Linear Increase ◽  
Clear Correlation ◽  
Slope Parameter ◽  
Sample Return ◽  
Opposition Effect ◽  
Imaging Camera ◽  
Small Phase ◽  
Solar System Bodies ◽  
Sample Return Mission ◽  
Phase Angles

Aims. The opposition effect has been detected on solar system bodies such as asteroids and comets. Two mechanisms have been proposed to explain the effect: the shadow-hiding opposition effect (SHOE) and the coherent backscattering opposition effect (CBOE). The Hayabusa asteroid sample return mission provides a unique opportunity to investigate the opposition effect on disk-resolved images of the S-type asteroid (25413) Itokawa at very small phase angles α. Methods. We made use of the data taken at α = 0.°04–2.°54 using the Asteroid Multi-band Imaging Camera (AMICA) on UT 2005 October 13. Comparing sets of two images taken at different phase angles, we derived the opposition slope parameter (SOE) that characterizes a linear increase in the reflectance I∕F per unit phase angle. Results. We found that (i) SOE is less dependent on the incidence and emission angles; (ii) the reflectance increases nonlinearly toward the opposition at small angles with α ≲ 1.°4, showing a good correlation between mean I∕F and SOE; and (iii) SOE becomes nearly constant at α ≳ 1.°4 and shows no clear correlation between I∕F and SOE. Conclusions. From these results, we conjecture that CBOE is dominant at α ≲ 1.°4, while SHOE is dominant at α ≳ 1.°4.

scholarly journals Phase-curve analysis of comet 67P/Churyumov-Gerasimenko at small phase angles

2019 ◽  
Vol 630 ◽  
pp. A11
Author(s):  
N Masoumzadeh ◽  
L Kolokolova ◽  
C Tubiana ◽  
M. R. El-Maarry ◽  
S Mottola ◽  
...  
Keyword(s):  
Phase Angle ◽  
Textural Properties ◽  
Phase Ratio ◽  
Phase Curve ◽  
Model Parameters ◽  
Study Phase ◽  
Opposition Effect ◽  
Small Phase ◽  
Phase Angles ◽  
Comet 67P

Aims. The Rosetta-OSIRIS images acquired at small phase angles in three wavelengths during the fly-by of the spacecraft on 9–10 April 2016 provided a unique opportunity to study the opposition effect on the surface of comet 67P/Churyumov-Gerasimenko (67P). Our goal is to study phase curves of the nucleus at small phase angles for a variety of surface structures to show the differences in their opposition effect and to determine which surface properties cause the differences. Methods. We used OSIRIS NAC images that cover the Ash-Khepry-Imhotep region to extract the phase curve, that is, the reflectance of the surface as a function of phase angle. We selected six regions of interest (ROIs) and derived the phase curves for each ROI. We fit a linear-exponential function to the phase curves. The resulting model parameters were then interpreted by spectrophotometric, geomorphological, and phase-ratio analyses, and by investigating the influence of structural and textural properties of the surface. Results. We find evidence for the opposition effect (deviation of the phase curve from linear behavior) in phase curves for all areas. We found an anticorrelation between the phase ratio and reflectance in a small phase angle range. This provides evidence for the shadow-hiding effect. We conclude that the decrease in the slope of the phase ratio versus reflectance indicates a decrease in the proportion of shadowed regions and reduces the contribution of the shadow-hiding effect. Large uncertainties in the determination of the opposition effect parameters with respect to wavelength do not allow us to conclusively claim coherent backscattering in the opposition effect phenomenon. Based on the two analyses, we conclude that the opposition effect of comet 67P in the Ash-Khepry-Imhotep region is mainly affected by shadow-hiding.

The VMC/VEx photometry at small phase angles: Glory and the physical properties of particles in the upper cloud layer of Venus

2015 ◽  
Vol 113-114 ◽  
pp. 120-134 ◽  
Author(s):  
Elena V. Petrova ◽  
Oksana S. Shalygina ◽  
Wojciech J. Markiewicz
Keyword(s):  
Physical Properties ◽  
Cloud Layer ◽  
Small Phase ◽  
Phase Angles

Photometry of particulate surfaces at extremely small phase angles

2007 ◽  
Vol 106 (1-3) ◽  
pp. 455-463 ◽  
Author(s):  
V. Psarev ◽  
A. Ovcharenko ◽  
Yu. Shkuratov ◽  
I. Belskaya ◽  
G. Videen
Keyword(s):  
Small Phase ◽  
Phase Angles
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